1. Field of the Invention
The present invention relates to a switch fabric system used in a packet switching device, and, in particular, to a technology that effectively prevents switching capacity of plural switches operating separately from each other from decreasing.
2. Description of the Related Art
In a network transmission device such as a router, a switch fabric system is used to switch variable-length packet data between functional blocks in the device. As a switching unit in one method for performing switching of a large-capacity line (high-speed line), there is a multi-plane cell switch fabric system (parallel switch) that includes M switch LSIs including a port of a speed of 1/M with respect to a required line speed that uses the switch LSIs in parallel, wherein the switch LSIs are operated at a relatively low speed.
As a multi-plane switch fabric technology in the related art, there is a system that uses plural ATM (Asynchronous Transfer Mode) switches in parallel as described in JP-A-5-327777. Since this system originally divides a fixed-length ATM cell into a number of sub-cells equal to the number of ATM switches in the system, cells can flow to all of the plural ATM switches. Therefore, it is possible to use the effective switching capacity of the switch fabric system until the switching capacity is equal to the maximum switching capacity. However, with a variable-length packet of Ethernet (registered trademark), etc., since a large number of non-effective parts occur among the sub-cells depending on the packet length, the effective switching capacity of the switch fabric system decreases. Moreover, since there is a need to completely synchronize all the ATM switches, when packets having a small grain size flow through the large-capacity line, it is difficult to process them.
A method of dividing a data stream into plural data blocks having a predetermined length L and dividing them into m sub-data blocks (bit slice) to transmit them to the plural ATM switches in parallel is disclosed in JP-A-6-187311. However, even in the case of using the above method, the number of divided sub-data blocks is not equal to the number of ATM switches, thus, the effective switching capacity decreases. Further, even if the number of resolved sub-data blocks is equal to the number of ATM switches, when the original data block is sufficiently smaller than L or somewhat larger than L, the effective switching capacity decreases due to padding in order to conform the data block length to L.
In WO02/43329, the same time stamp in addition to an address number, a transmission source number, and a cell dividing number is added to the cell generated from the same packet and the cells are distributed to the plural switching units. A method of allowing the switching unit to preferentially select old time stamps and a reordering unit to sequentially reassemble cells and packets belonging to the same flow in order from the time stamps having old values is disclosed. With the above method, the multi-plane switch fabric system can be configured by using any number of asynchronously operating switching units; however, the exchanging capacity of the switch fabric system decreases depending on the packet length.